2.1 Earth's Crust in Motion

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Vocabulary

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Earthquake: The shaking and trembling that happens to the movement of rock beneath Earth's surface.
Stress: A force that can change the shape or volume of a rock.
Shearing: Stress that pushes chunks of rock in two opposite directions.
Tension: A stress force that pulls on the crust, stretching rock so that it becomes thinner in the middle, and then breaks.
Compression: The stress force that squeezes rock until it breaks.
Deformation: Any change in volume or shape of Earth's Crust.
Fault: A crack in Earth's Crust where slabs of crust have slipped past each other.
Strike-Slip Fault: Where rocks on either sides of the fault slip past each other, with a little up-or-down motion.
Normal Fault: When the fault is at an angle, so one block of rock lies above the fault, while the other block lies below the fault.
Hanging Wall: When half of the fault lies above the fault.
Footwall: When half of the fault lies below.
Reverse Fault: When blocks of rock move in opposite directions, like a divergent boundary.
Fault-block mountains: When a normal fault uplifts a block of rock.
Folds: Bends in rock that form when compression shortens and thickens part of Earth's crust.
Anticline: A fold in rock that bends upward into an arch.
Syncline: A fold in rock that bends downward in the middle, to form a bowl.
Plateau: A large area of land that is above sea level.

Outline

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Stress in the Crust

• Movement of Earth's plates create powerful forces that squeeze/pull rock in the crust, stress
• stress is a force, so it adds energy to the rock. Energy is stored until rock breaks/changes shape

Types of Stress

• Three types of stress: shearing, tension, and compression, work over millions of years to change the shape and volume of rock
• these forces cause some rock to become brittle and snap, some rocks bend like melted road tar
  • Tension stretches rock like stretching chewed bubble gum, occurs when two plates are moving apart
  • Compression squeezes rock together until it folds/breaks
  • Plates move very slowly, causes deformation

Kinds Of Faults

• When enough stress builds up in rock, the rock breaks, making a fault
• Faults usually occur along plate boundaries, where plate motion forces compress/pull/shear so much that crust breaks
• Three faults: strike slip, normal, and reverse

Strike-Slip Faults

• Rocks on each side of fault slip past each other sideways, little up-or-down motion
• A strike-slip fault is called a transform boundary where the plates meet

Normal Faults

• Caused by tension forces in crust
• The fault is at an angle
  • on block above fault, one block below fault
    • Block above is the hanging wall
    • Block below is footwall
• When movement occurs, hanging walls slips downward

Reverse Faults

• Hanging wall moves over footwall
  • kind of like the opposite of a normal fault.

Friction Along Faults

• Low friction, fault easily moves. High friction:Plates stick together, storing energy.
  • In earthquakes, stored energy from the plates with high friction finally release when plates eventually move.

Mountain Building

• fault movement can change a flat surface into a tall mountain range. (over millions of years)

Mountains Formed by Faulting

• Formed when a normal fault uplifts a block of rock
  • when two normal faults are next to each other, the rock left behind forms a mountain.
    • mountains formed like this are in many places.

Mountains Formed By Folding

• Formed when rock wrinkles together, like skidding on a rug.
  • many big mountain ranges have been created by folding.

Anticlines And Synclines

• look like ocean waves, a bowl
  • formed by compression and folding of crust over millions of years.

Plateaus

• Same force that raises mountains can make plateaus
  • plateaus are like tables, wider than they are tall
  • many places have plateaus

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